meson: Decouple linux/dma-buf.h and libdrm checks

Currently dmabuf_dep is found when the following conditions are met:
 - linux/dma-buf.h is present;
 - libdrm is found.

This is because Linux dmabuf support requires drm_fourcc.h which is part
of libdrm.

However, dmabuf_dep is used for two purposes:
 - define HAVE_DMABUF to state dmabuf support;
 - ensure the presence of drm_fourcc.h for gdk and for the
   media-gstreamer module.

Decouple this, unconditionally check for libdrm and require it on
Linux. Then, use libdrm_dep only to state the drm_fourcc.h presence.

Given that now we unconditionally require libdrm on Linux, HAVE_DMABUF
depends only on the linux/dma-buf.h presence.

gdk/gdkdmabuffourccprivate.h

@@ -1,7 +1,7 @@
 #pragma once
 
 #include "config.h"
-#ifdef HAVE_DMABUF
+#ifdef HAVE_DRM_FOURCC_H
 #include <drm_fourcc.h>
 #endif
 

gdk/meson.build

@@ -219,7 +219,7 @@ gdk_deps = [
   platform_gio_dep,
   pangocairo_dep,
   vulkan_dep,
-  dmabuf_dep,
+  libdrm_dep,
   png_dep,
   tiff_dep,
   jpeg_dep,

meson.build

@@ -628,19 +628,17 @@ else
   vulkan_pkg_found = false
 endif
 
-if cc.has_header('linux/dma-buf.h')
-  dmabuf_dep = dependency('libdrm',
-    required: os_linux)
-else
-  if os_linux
-    error('OS is Linux, but linux/dma-buf.h not found.')
-  endif
-  dmabuf_dep = dependency('', required: false)
-endif
-cdata.set('HAVE_DMABUF', dmabuf_dep.found())
+libdrm_dep = dependency('libdrm', required: os_linux)
 # We only care about drm_fourcc.h for all the fourccs,
 # but not about linking to libdrm
-dmabuf_dep = dmabuf_dep.partial_dependency(includes: true, compile_args: true)
+libdrm_dep = libdrm_dep.partial_dependency(includes: true, compile_args: true)
+cdata.set('HAVE_DRM_FOURCC_H', libdrm_dep.found())
+
+has_linux_dma_buf_h = cc.has_header('linux/dma-buf.h')
+if os_linux and not has_linux_dma_buf_h
+  error('OS is Linux, but linux/dma-buf.h not found.')
+endif
+cdata.set('HAVE_DMABUF', has_linux_dma_buf_h)
 
 cloudproviders_dep = dependency('cloudproviders',
   required: get_option('cloudproviders'),

modules/media/meson.build

@@ -24,7 +24,7 @@ if gstplayer_dep.found() and gstgl_dep.found()
   cdata.set('HAVE_GSTREAMER', 1)
   media_gst_deps = [ libm, libgtk_dep, gstplayer_dep, gstgl_dep ]
 
-  if dmabuf_dep.found() and gstdrm_dep.found()
+  if libdrm_dep.found() and gstdrm_dep.found()
     cdata.set('HAVE_GSTREAMER_DRM', 1)
     media_gst_deps += [ gstdrm_dep ]
   endif